Joining California in filing the lawsuit are the attorneys general of Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon, and Virginia.

Mr Trump declared a national emergency to fulfil his promise of completing the wall.

The move allows the president to bypass Congress to use money from the Pentagon and other budgets.

California has repeatedly challenged Mr Trump in court.

I’ll tell you what’s an emergency:

Separated familiesGun violenceClimate change

Those are some real emergencies we're facing — not a pointless border wall.